1. Field of the Invention
The present invention relates to a digital DC-DC converter and a power source circuit and a semiconductor device that includes the DC-DC converter.
2. Description of the Related Art
A DC-DC converter is a constant-voltage circuit with which a constant output voltage can be obtained regardless of the value of an input voltage, and the DC-DC converter is used for a power supply circuit together with a rectification circuit or the like. In particular, a power supply circuit including a switching type DC-DC converter is referred to as a switching power source or a switching regulator.
The switching type DC-DC converter outputs a voltage with a predetermined value in such a manner that a voltage with a pulse waveform is formed using an input voltage by a switching element and the voltage is smoothed or held in a coil, a capacitor, or the like. A proportion of a period in which the switching element is on, what is called a duty ratio, is controlled by a control circuit in the DC-DC converter. By the control of the duty ratio using the control circuit, the value of an output voltage can be controlled.
Among DC-DC converters, analog DC-DC converters in which a control circuit is formed using an analog circuit have been the mainstream. However, in recent years, a digital DC-DC converter including a signal processing circuit such as a digital signal processor (the DSP) as a control circuit has been practically used. The digital DC-DC converter can perform high-speed switching of a switching element, have high accuracy of signal processing in the control circuit, and have the control circuit with a simple structure.
Patent Document 1 discloses a power source control in a digital manner.